Impressed current cathodic protection (ICCP) uses the principle of cathodic protection to protect large metal objects in corrosive situations like ships or underground tanks. As a quick reminder from the second article in this series, cathodic protection uses the galvanic reaction as a benefit to protect smaller metals items. ICCP is used when the items needing protection are especially large or when fine-tuned control of the galvanic reaction is needed, as can be the case with ships which enter waters of varying salinity.
The generic impressed current system uses rod-shaped anodes of graphite or platinum immersed in the electrolyte solution, e.g. the ocean or underground. The anodes are connected electrically to a DC power source, which could be a solar panel, a generator, or rectified AC power. The power source then connects to the item to be protected, like the hull of a ship or an underground pipeline, which acts as the cathode in the circuit. The DC power assures that the current will always move in the right direction so that the cathode metal will be protected from degradation. Certain anodes, like platinum, also have the advantage of degrading so little that they never need replacing.
Here's a quick video by CorrConnect on how it works.
ICCP systems range from a simple set-up as shown in the video which is more suited to underground pipes and tanks, to much more complex systems involving different kinds and shapes of anodes and more specific styles of connectors as are needed for protecting ship drive-shafts. Needless to say, these larger systems can cost a pretty penny and require regular maintenance. This picture from Cathodic Marine Engineering shows one of these more complex systems.
Check out this video to learn more about corrosion: